1. Field of the Invention
The present invention relates generally to a wireless power transmitter and a method for controlling the same, and more particularly, to a wireless power transmitter for transmitting charging power to a wireless power receiver, and a method for controlling the same.
2. Description of the Related Art
A mobile terminal, such as a cellular phone or a Personal Digital Assistant (PDA), is powered by a rechargeable battery facilitate to its mobility. In order to charge the battery, electrical energy is supplied to the battery of the mobile terminal using a separate charging device. Typically, the charging device and the battery have separate contact terminals mounted on outer surfaces thereof, such that they may be electrically connected when their contact terminals contact each other.
However, in this contact charging technique, since the contact terminals protrude outside, they are apt to be contaminated by rogue (or foreign) substances, causing a failure in battery charging. The battery charging may fail even if the contact terminals are exposed to moisture.
In order to address these and other disadvantages, wireless charging or contactless charging technologies have been developed and used in many electronic devices.
In the wireless charging technology that uses wireless power transmission/reception, a battery of a mobile terminal may be automatically charged if the mobile terminal is simply placed on a charging pad without being connected to a charging device via a separate charging connector. Generally, the wireless charging technology is well known to the public and may improve the portability of electronic devices due to eliminating the need for a wired charger. As a result, the related technologies are expected to significantly evolve even in the coming electric car era.
These wireless charging technologies may be roughly classified into a coil-based electromagnetic induction scheme, a resonance scheme, and a radio radiation scheme (also known as an Radio Frequency (RF)/micro wave radiation scheme) that delivers electrical energy by converting it into microwaves.
Up to the present, the electromagnetic induction scheme has mainly been used. However, as experiments involving wirelessly transmitting power over distances of tens of meters using microwaves have been successful, the possibility exists that all electronic products may be wirelessly charged anytime and anywhere in the near future.
The electromagnetic induction-based power transmission method is a scheme of transmitting power between a primary coil and a secondary coil. If a magnet moves around a coil, an induced current occurs. Based on this principle, a transmitter generates a magnetic field, and a receiver generates electrical energy as a current is induced due to a change in the magnetic field. This phenomenon is called an electromagnetic induction phenomenon, and the electromagnetic induction-based power transmission method has excellent energy transfer efficiency.
The resonance scheme provides a system in which electricity may be wirelessly transferred to an electronic device using the resonance-based power transmission principle even though the electronic device is at a distance of several meters from a charging device. This wireless charging system is based on the physics concept called ‘resonance’, in which electromagnetic waves containing electrical energy are caused to resonate. The resonating electrical energy may be directly delivered only to an electronic device having a resonant frequency, and the unused electrical energy may be re-absorbed as an electromagnetic field instead of being spread into the air. Therefore, unlike the electromagnetic waves, the electrical energy does not seem to affect the nearby machine and human bodies.
Although many studies on wireless charging schemes have been made, no standard has been proposed for, for example, wireless charging priority, search for a wireless power transmitter/receiver, selection of a communication frequency between a wireless power transmitter and a wireless power receiver, adjustment of wireless power, selection of a matching circuit, and distribution of a communication time for each of wireless power receivers in one charging cycle. In particular, there is a need for a standard for the configuration and procedure in which a wireless power receiver selects a wireless power transmitter from which the wireless power receiver will receive wireless power.
In particular, there is a need for the development of new technology for efficiently determining whether a rogue object is withdrawn or removed, if an error occurs while a wireless power receiver or the rogue object is placed on the wireless power transmitter.